1. Technical Field
The present invention relates to an absorption heat pump for converting heat of a heat source such as waste hot water, exhaust gas or waste steam (waste heat energy) into heat of a high-temperature medium (such as high-temperature water or high-temperature steam). In particular, the present invention relates to an absorption heat pump for obtaining a high-temperature heat receiving medium vapor using a heating source as above. The present invention also relates to an absorption heat pump with improved thermal efficiency, and, in particular, to a two-stage absorption heat pump with improved start-up characteristics.
2. Related Art
There are the following types of absorption heat pumps which use waste hot water as a heat source to generate hot water with a temperature higher than that of the waste heat source. FIG. 31 is a view illustrating an example of the constitution of a single-stage absorption heat pump. As shown in the drawing, the single-stage absorption heat pump has an absorber A, an evaporator E, a generator G, a condenser C and a solution heat exchanger X as primary components. A cooling water pipe 101, a hot water pipe 102, a hot water pipe 103 and a high-temperature hot water pipe 104 are disposed in the condenser C, the evaporator E, the generator G and the absorber A, respectively.
Dilute solution (working medium dilute solution) is heated by heat source hot water flowing through the hot water pipe 103 in the generator G and concentrated into concentrated solution (working medium concentrated solution). The concentrated solution is delivered to the solution heat exchanger X through a concentrated solution pipe 106 by a solution pump 105, heated therein, and fed to the absorber A. Vapor (working medium vapor) generated in the generator G is fed to the condenser C through a vapor pipe 110, cooled by cooling water flowing through the cooling water pipe 101 and condensed into refrigerant liquid (working medium refrigerant liquid) in the condenser C. The refrigerant liquid is fed to the evaporator E through a refrigerant pipe 108 by a refrigerant pump 107. The refrigerant liquid is heated by heat source hot water flowing through the hot water pipe 102 and evaporated into refrigerant vapor (working medium refrigerant vapor) in the evaporator E. The refrigerant vapor is fed to the absorber A through a vapor pipe 109 and absorbed into the concentrated solution supplied from the generator G in the absorber A.
In the absorber A, the concentrated solution is heated by the heat of absorption generated when the refrigerant vapor is absorbed into the concentrated solution, rises in temperature to the degree corresponding to the boiling point elevation and heats the high-temperature hot water pipe 104. Therefore, water flowing through the high-temperature hot water pipe 104 is heated, and hot water with a temperature higher than that of the heat source hot water can be obtained: Dilute solution into which the concentrated solution turns upon the absorption of the refrigerant vapor in the absorber A is supplied to the solution heat exchanger X through a dilute solution pipe 112 to heat the concentrated solution in the heating side of the solution heat exchanger X and returns to the generator G through a pressure reducing valve 113. The refrigerant vapor generated in the generator G is directed to the condenser C, and cooled and condensed by cooling water flowing through the cooling water pipe 101 as described before. Then, the same cycle is repeated.
FIG. 32 is a view illustrating an example of the constitution of a two-stage absorption heat pump. As shown in FIG. 32, the two-stage absorption heat pump has a high-temperature absorber A2, a low-temperature absorber A1, a high-temperature evaporator E2, a low-temperature evaporator E1, a generator G, a condenser C, a high-temperature solution heat exchanger X2, and a low-temperature solution heat exchanger X1 as primary components.
As equipment on the solution side, there are a solution pump 205 for feeding the concentrated solution in the generator G to the high-temperature absorber A2, a concentrated solution pipe 206, a dilute solution pipe 215, a medium-concentration dilute solution pipe 214, a first pressure reducing valve 216, a second pressure reducing valve 226, a first hot water pipe 203 disposed in the generator G, a control valve 228 disposed in the first hot water pipe 203 at a position near the inlet thereof, a second hot water pipe 204 disposed in the high-temperature absorber A2, a temperature sensor 229 disposed in the second hot water pipe 204 at a position near the outlet thereof for detecting the outlet temperature of the second hot water pipe 204, a liquid level sensor 227 for detecting the liquid level in the low-temperature absorber A1, a first spray 224 opening in the low-temperature absorber A1, and a second spray 223 opening in the high-temperature absorber A2.
As equipment on the refrigerant side, there are a refrigerant pump 208 for feeding a refrigerant from the condenser C to the low-temperature evaporator E1 and the high-temperature evaporator E2, refrigerant pipes 209, 210 and 211, a spray 218 opening in the low-temperature evaporator E1, a spray 219 opening in the high-temperature evaporator E2, a liquid level sensor 220 for detecting the liquid level in the low-temperature evaporator E1, a liquid level sensor 230 for detecting the liquid level in the high-temperature evaporator E2, a control valve 221 for controlling the flow rate of the refrigerant to be supplied to the spray 218, a control valve 222 for controlling the flow rate of the refrigerant to be supplied to the spray 219, a cooling water pipe 201 disposed in the condenser C, a third hot water pipe 202 disposed in the low-temperature evaporator E1, and a control valve 225 disposed at the inlet of the third hot water pipe 202.
As equipment for connecting the solution side and the refrigerant side, there are a vapor pipe 207 for directing refrigerant vapor generated in the generator G to the condenser C, a vapor pipe 212 for directing refrigerant vapor generated in the low-temperature evaporator E1 to the low-temperature absorber A1, a vapor pipe 213 for directing refrigerant vapor generated in the high-temperature evaporator E2 to the high-temperature absorber A2, and a heat transporting pipe 217 connecting the low-temperature absorber A1 and the high-temperature evaporator E2 and having a loop passage for supplying heat obtained in the low-temperature absorber A1 to the high-temperature evaporator E2 with water circulating in it. The control valves 228 and 225 are controlled based on a detection signal from the temperature sensor 229 disposed in the second hot water pipe 204 at an outlet side position thereof.
Hot water such as waste hot water is supplied as heat source hot water to the first hot water pipe 203 and the third hot water pipe 202, and the temperature of a heat transfer medium is increased in two stages using thermal energy derived from the difference in temperature between the hot water and cooling water supplied to the cooling water pipe 201 in the condenser C and utilizing heat of absorption and boiling point elevation of solution to increase the temperature in the high-temperature absorber A2 to a considerably high level. Then, hot water separately supplied to the second hot water pipe 204 is heated and high-temperature hot water with a great deal of potential, which cannot be obtained in a conventional cycle, can be obtained.
In the generator G, the dilute solution (working medium dilute solution) is heated by the heat source hot water flowing through the first hot water pipe 203 and concentrated into concentrated solution (working medium concentrated solution). The concentrated solution is delivered by the solution pump 205 through the concentrate solution pipe 206, heated in the heated side of the low-temperature solution heat exchanger X1 and the heated side of the high-temperature solution heat exchanger X2 and fed to the high-temperature absorber A2. Refrigerant vapor (working medium vapor) generated in the generator G is fed to the condenser C through a vapor pipe 207, cooled by cooling water flowing through the cooling water pipe 201 and condensed into refrigerant liquid (working medium cooling liquid) in the condenser C. The refrigerant liquid is delivered to the low-temperature evaporator E1 and the high-temperature evaporator E2 through the refrigerant pipes 209, 210 and 211 by the refrigerant pump 208. The refrigerant liquid in the low-temperature evaporator E1 is heated by heat source hot water flowing through the third hot water pipe 202 and evaporated into refrigerant vapor (working medium vapor). The refrigerant vapor is fed to the low-temperature absorber A1 through the vapor pipe 212. The refrigerant liquid in the high-temperature evaporator E2 is heated by the heat transported from the low-temperature absorber A1 through the heat transporting pipe 217 and evaporated into refrigerant vapor (working medium vapor). The refrigerant vapor is fed to the high-temperature absorber A2 through the vapor pipe 213.
In the high-temperature absorber A2, the refrigerant vapor from the high-temperature evaporator E2 is absorbed into the concentrated solution from the generator G. The concentrated solution is heated by the heat of absorption generated when the refrigerant vapor is absorbed into the concentrated solution, rises in temperature to the degree corresponding to the boiling point elevation and heats the second hot water pipe 204. Therefore, water flowing through the second hot water pipe 204 is heated, and hot water with a temperature higher than that of the heat source hot water can be obtained. Medium-concentration solution into which the concentrated solution turns upon the absorption of the refrigerant vapor in the high-temperature absorber A2 flows to the high-temperature solution heat exchanger X2 through a medium-concentration solution pipe 214 to heat the concentrated solution from the generator G and is fed to the low-temperature absorber A1. In the low-temperature absorber A1, the medium-concentration solution absorbs the refrigerant vapor from the low-temperature evaporator E1 and turns into dilute solution. The dilute solution flows to the low-temperature solution heat exchanger X1 through a dilute solution pipe 215, heats the concentrated solution from the generator G in the low-temperature solution heat exchanger X1, and returns to the generator G through the first pressure reducing valve 216. The heat of absorption generated in the low-temperature absorber A1 when the medium-concentration solution absorbs the refrigerant vapor is transported to the high-temperature evaporator E2 through the heat transporting pipe 217. The vapor generated in the generator G is directed to the condenser C, and cooled and condensed by cooling water flowing through the cooling water pipe 201 as described before. Then, the same cycle is repeated.
The graph of absorption cycle of the flow on the solution side (which is hereinafter referred to as “series flow”) in the two-stage absorption heat pump constituted as described above is shown in FIG. 33. In the series flow, when a pressure distribution as a heat pump is achieved in every component after the start-up has been completed and normal operation has begun, a normal solution circulation system is established. That is, the concentrated solution generated in the generator G is fed to the high-temperature absorber A2 with a high refrigerant vapor pressure by the pump 205, the medium-concentrated solution flows from the high-temperature absorber A2 to the low-temperature absorber A1 by the difference in refrigerant vapor pressure between the high-temperature absorber A2 and the low-temperature absorber A1, and the dilute solution generated in the low-temperature absorber A1 flows from the low-temperature absorber A1 to the generator G by the difference in refrigerant vapor pressure between the low-temperature absorber A1 and the generator G.
FIG. 34 and FIG. 35 show the graph of absorption cycle in the case of a reverse flow pattern (which is hereinafter referred to as “reverse flow”) and the graph of absorption cycle in the case of a parallel flow pattern (which is hereinafter referred to as “parallel flow”). In these cases, since solution is introduced into the low-temperature absorber A1 at the start of operation, the refrigerant in the low-temperature absorber A1 becomes higher in temperature than the refrigerant in the low-temperature evaporator E1 and circulation of the solution can be achieved.
However, since the absorption heat pumps obtain high-temperature heat in the form of high-temperature water (sensible heat) as heat receiving fluid, high pump power is necessary to circulate the high-temperature water. Also, in the known absorption heat pumps, the heat receiving medium liquid is heated, but they are not to produce vapor of the receiving medium. Thus, preheating of the heat receiving medium is not taken into account.
In addition, in the conventional single-stage absorption heat pumps and two-stage absorption heat pumps, preheating of the condensed medium (working medium condensed solution) to be fed from the condenser C to the evaporators E, E1, and E2 is not taken into account. Thus, an absorption heat pumps with high efficiency cannot be obtained.
Moreover, in the series flow, since no solution has been supplied to the low-temperature absorber at start-up, the cooling medium in the low-temperature absorber A1 is heated by the heat of condensation of the refrigerant vapor from the low-temperature evaporator E1. Thus, the temperature of the cooling medium is lower than the evaporation temperature in the low-temperature evaporator E1. The cooling medium is used as a heat source to generate refrigerant vapor or the cooling medium itself turns into refrigerant vapor in the high-temperature evaporator E2, and the refrigerant vapor is absorbed into the concentrated solution in the high-temperature absorber A2. Thus, the refrigerant vapor pressure in the high-temperature absorber A2 is lower than the vapor pressure in the low-temperature absorber A1 (equal to the vapor pressure in the low-temperature evaporator E1), and the medium-concentration solution cannot flow from the high-temperature absorber A2 to the low-temperature absorber A1 without reliance on the potential head difference. Therefore, when the height of the high-temperature absorber A2 is not high enough, the absorption heat pump cannot be started or it takes a long time to start the absorption heat pump.
In the reverse flow shown in FIG. 34, two solution pumps are required. In the parallel flow shown in FIG. 35, only one solution pump may be enough. However, the concentration ranges in the low-temperature absorber A1 and the high-temperature absorber A2 are wide and the concentrations at the outlets of the absorbers are generally equal to the concentration of the dilute solution. Thus, the solution temperature at the outlets of the absorbers is lower than those in the series flow shown in FIG. 33 and the flow shown in FIG. 34. That is, the temperature raising performance as a heat pump is low.
The present invention has been made in view of the above points. It is, therefore, an object of the present invention to provide an absorption heat pump in which waste hot water, exhaust gas or waste steam is used as a heat source for heating heat receiving medium liquid to produce vapor of the heat receiving medium in order to reduce the auxiliary machine power and in which the heat receiving medium liquid is preheated to improve the efficiency in converting the heat receiving medium liquid into vapor.
Another object of the present invention is to provide an absorption heat pump in which a condensed refrigerant (working medium condensed solution) to be supplied from a condenser to an evaporator is preheated to improve the efficiency.
Another object of the present invention is to provide a two-stage absorption heat pump which is low in height and excellent in the temperature raising performance and start-up characteristics and with which a high-temperature medium can be obtained in the form of high-temperature vapor.